Relationship of nutrient dynamics and bacterial community structure at the water-sediment interface using a benthic...

The relationships between nutrient dynamics and the bacterial community at the water-sediment interface were investigated using the results of nutrient release fluxes, bacterial communities examined by 16S rRNA pyrosequencing and canonical correlation analysis (CCA) accompanied by lab-scale benthic chamber experiment. The nutrient release fluxes from the sediments into the water were as follows: -3.832 to 12.157 mg m^-2 d^-1 for total phosphorus, 0.049 to 9.993 mg m^-2 d^-1 for PO₄-P, -2.011 to 41.699 mg m^-2 d^-1 for total nitrogen, -7.915 to -0.074 mg m^-2 d^-1 for NH₃-N, and -17.940 to 1.209 mg m^-2 d^-1 for NO₃-N. To evaluate the relationship between the bacterial communities and environmental variables, CCA was conducted in three representative conditions: in the overlying water, in the sediment at a depth of 0-5 cm, and in the sediment at a depth of 5-15 cm. CCA results showed that environmental variables such as nutrient release fluxes (TN, NH₄, NO₃, TP, and PO₄) and water chemical parameters (pH, DO, COD, and temperature) were highly correlated with the bacterial communities. From the results of the nutrient release fluxes and the bacterial community, this study proposed the hypothesis for bacteria involved in the nutrient dynamics at the interface between water and sediment. In the sediment, sulfate-reducing bacteria (SRB) such as Desulfatibacillum, Desulfobacterium, Desulfomicrobium, and Desulfosalsimonas are expected to contribute to the decomposition of organic matter, and release of ammonia (NH₄⁺) and phosphate (PO₄^3-). The PO₄^3- released into the water layer was observed by the positive fluxes of PO₄^3-. The NH₄⁺ released from the sediment was rapidly oxidized by the methane-oxidizing bacteria (MOB). This study observed in the water layer dominantly abundant MOB of Methylobacillus, Methylobacter, Methylocaldum, and Methylophilus. The nitrate (NO₃^-) accumulation caused by the oxidation environment of the water layer moved back to the sediment, which led to the relatively large negative fluxes of NO₃^-, compared to the small negative fluxes of NH₄⁺.